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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id k70sm35258535pgd.19.2022.01.04.14.25.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Jan 2022 14:25:04 -0800 (PST) Date: Tue, 4 Jan 2022 22:25:01 +0000 From: Sean Christopherson To: Maxim Levitsky Cc: kvm@vger.kernel.org, Jim Mattson , Thomas Gleixner , Joerg Roedel , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Vitaly Kuznetsov , Borislav Petkov , linux-kernel@vger.kernel.org, Paolo Bonzini , Dave Hansen , "H. Peter Anvin" , Wanpeng Li , Ingo Molnar Subject: Re: [PATCH v2 2/5] KVM: SVM: allow to force AVIC to be enabled Message-ID: References: <20211213104634.199141-1-mlevitsk@redhat.com> <20211213104634.199141-3-mlevitsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211213104634.199141-3-mlevitsk@redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Dec 13, 2021, Maxim Levitsky wrote: > Apparently on some systems AVIC is disabled in CPUID but still usable. > > Allow the user to override the CPUID if the user is willing to > take the risk. > > Signed-off-by: Maxim Levitsky > --- > arch/x86/kvm/svm/svm.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index c9668a3b51011..468cc385c35f0 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -206,6 +206,9 @@ module_param(tsc_scaling, int, 0444); > static bool avic; > module_param(avic, bool, 0444); > > +static bool force_avic; > +module_param_unsafe(force_avic, bool, 0444); > + > bool __read_mostly dump_invalid_vmcb; > module_param(dump_invalid_vmcb, bool, 0644); > > @@ -4656,10 +4659,14 @@ static __init int svm_hardware_setup(void) > nrips = false; > } > > - enable_apicv = avic = avic && npt_enabled && boot_cpu_has(X86_FEATURE_AVIC); > + enable_apicv = avic = avic && npt_enabled && (boot_cpu_has(X86_FEATURE_AVIC) || force_avic); > > if (enable_apicv) { > - pr_info("AVIC enabled\n"); > + if (!boot_cpu_has(X86_FEATURE_AVIC)) { > + pr_warn("AVIC is not supported in CPUID but force enabled"); > + pr_warn("Your system might crash and burn"); > + } else Needs curly braces, though arguably the "AVIC enabled" part should be printed regardless of boot_cpu_has(X86_FEATURE_AVIC). > + pr_info("AVIC enabled\n"); This is all more than a bit terrifying, though I can see the usefuless for a developer. At the very least, this should taint the kernel. This should also probably be buried behind a Kconfig that is itself buried behind EXPERT.